Chapter 29: Development

Define the embryonic period

extends from fertilization thru the 8th week of development

define fertilization

merging of genetic info from haploid sperm & haploid secondary oocyte

Trace the path of sperm fertilizing the secondary oocyte

1. swim from vagina → cervix

2. pass thru the uterus & uterine tubes

3. penetrate the corona radiata → zona pellucida → plasma membrane of the secondary oocyte → cytoplasm of secondary oocyte

The ____ of the sperm’s acrosome, along w/ _________, allow the sperm to penetrate the corona radiata

enzymes

tail movement

As the sperm penetrates the secondary oocyte, ________ in the zona pellucida is a receptor for the sperm. Membrane proteins in the sperm head bind to this receptor, & acrosomal enzymes are released to digest a path in the zona pellucida.

Glycoprotein ZP3

During fertilization, the haploid nucleus in the head of the sperm becomes the _______, and the haploid nucelus of the fertilized ovum becomes the _________. When the 2 merge (syngamy), the ________ is formed.

male pronucleus

female pronucleus

diploid zygote

Define cleavage

mitotic division of the zygote that begins ~24 hrs after fertilization

Describe cleavage (day 1)

Describe cleavage (day 2)

by 2nd day after fertilization, 2nd cleavage is completed, yielding 4 cells

Describe cleavage (day 3)

by end of 3rd day, there are 16 cells

• each division yields smaller & smaller cells → blastomeres

Describe cleavage (day 4)

by 4th day, the cluster of cells resembles a mulberry → morula

• (still surrounded by zona pellucida & is still the size of a zygote)

Describe cleavage (day 4-5)

• morula enters uterine cavity & is nourished by uterine milk (a glycogen-rich secretion from endometrial glands in addition to stored nutrients from the cytoplasm)

• 32-cell stage → the fluid now inside the morula rearranges the blastomeres into a large, fluid-filled blastocyst cavity (blastocoel)

  • the mass is now called a blastocyst (still the same size as the OG zygote)

As the blastocyst formed, 2 diff. cell populations arose:

1. Embryoblast → (inner cell mass) will develop into the embryo

2. Trophoblast → (outer cell mass) will develop into the outer chorionic sac surrounding the fetus, & the fetal portion of the placenta

The blastocyst remains free in the uterine cavity for ~2 days, then implants by attaching to the ________ at ~6 days after fertilization

endometrium

implantation usually occurs in either the _________ or the __________. The inner cell mass (embryoblast) orients toward the _______

posterior portion of the fundus

body of the uterus

endometrium

After implantation, the endometrium is called the _______. This structure separates from the endometrium after the fetus is delivered.

decidua

Name the different regions of the decidua

1. basal decidua

2. capsular decidua

3. parietal decidua

Summarize the events during the 1st week of development

1. FERTILIZATION → occurs within uterine tube 12-24 hrs after ovulation

2. CLEAVAGE → 1st cleavage completed ~30 hrs after fertilization

3. MORULA → 3-4 days after fertilization

4. BLASTOCYST → 4.5-5 days after fetiliztion

5. IMPLANTATION → ~6 days after fertilization

After ~8 days after implantation, the trophoblast develops into the _________ & __________

synctiotrophoblast

cytotrophoblast

At ~8 days, the embryoblast also develops into 2 layers: the _________ & _________. Cells of these structures form a flat disc called the _________.

hypoblast (primitive endoderm)

epiblast (primitive ectoderm)

bilaminar embryonic disc

The ______ forms the epiblast

amniotic cavity

Also on the 8th day, the exocoelomic membrane forms, which, tgt w/ the hypoblast, forms the _______

yolk sac

On day 9, small spaces called ______ form

lacunae

By the 12th day, the lacunae fuse to form ______

lacunar networks

On the 12th day after fertilization, the ____________ develops. The cells form a CT layer around the ____ and _______

extraembryonic mesoderm

amnion

yolk sac

The extraembryonic mesoderm and the trophoblast, together, form the ______, which surrounds the ____ & later, the _____.

chorion

embryo

fetus

Describe the 3 main functions of the chorion

1. blocks antibody production by the mother

2. promotes production of T lymphocytes to suppress the immune response in the uterus

3. produces human chorionic gonadotropin (hCG)

The first major event of the 3rd week of development is _________

gastrulation

Define gastrulation

• the bilaminar embryonic disc tranforms into a trilaminar embryonic disc (ectoderm, mesoderm, endoderm)

• associated w/ the rearrangement & migration of cells from the epiblast

Describe the events of gastrulation

• 1st step → formation of the primitive streak

  • establishes the head & tail ends of the embryo

• 2nd step → cells of the epiblast move inward below the primitive streak & undergo invagination

  • the 3 germ layers form:

    • endoderm

    • mesoderm

    • ectoderm

~16 days after fertilization, the _____ process forms. By days 22-24, this process becomes the _____

notochordal

notochord

Describe the functions of the notochord

• induction → process whereby the inducing tissue stimulates development of a responding tissue to develop into a specific structure (e.g development of…

  • vertebral bodies

  • neural plate (forms the neural tube))

At ~4 weeks after fertilization, the head end of the _______ develops into 3 enlarged areas called __________.

neural tube

primary brain vesicles

Explain the significance of neurulation

1. Formation of the CNS → neurulation creates the neural tube, which becomes the brain & spinal cord

2. Neural crest cell development

3. Establishes the embryo’s head-to-tail axis

List the primary brain vesicles

1. Prosencephalon (forebrain)

2. Mesencephalon (midbrain)

3. Rhombencephalon (hindbrain)

At ~17th day after fertilization, paired, cube-shaped structures called _______ form

somites

Each somite differentiates into a ________, a ________, & a ________

1. myotome (neck, trunk, & limb)

2. dermatome

3. sclerotome (vertebrae/ribs)

On days 18 & 19, the heart begins to develop in the head end of the embryo in a region of mesodermal cells called the ________. ______ Embryonic tissue invades the uterine wall & erodes uterine blood vessels, developing ______

cardiogenic area

chrionic villi

By the end of the 3rd week, blood vessels develop in the _____ & connect to the embryonic heart. The vessels connecting to the heart do so by way of the _______ & _________ through the connecting stalk which eventually becomes the ________

chorionic villi

umbilical arteries

umbilical vein

umbilical cord

Define placentation and placenta

placentation → process of forming the placenta

placenta → site of exchange of nutrients & wastes between mother & fetus; produces hormones used to sustain the pregnancy

By the beginning of the 12th week, the placenta has 2 parts:

1. fetal portion (chorionic villi)

2. maternal portion (decidua basalis of the endometrium)

All major organs develop between the 4th-8th week (AKA _______)

organogenesis

_________ (when the flat embryo folds into a 3D cylinder) occurs during the 4th week

embryonic folding

During embryonic folding, lateral folds form and , as they move toward the midline, they incorporate the ______ into the embryo as the _________

yolk sac

primitive gut

On the outside of the embryo is a cavity in the tail region called the ______

proctodeum

Separating the cloaca from the proctodeum is the _______

cloacal membrane

5 pairs of _________ develop on each side of the future head & neck regions of the embryo during the 4th week

pharyngeal arches/clefts (branchial arches)

By the ___ week, the regions of the limbs become distinct & digits appear

7th

Describe the fetal period

• begins at 9th week after fertilization

• tissues & organs that developed during the embryonic period grow & differentiate

• very few new structures appear during this period

Any agentor influence that is able to cause developmental defects in an embryo or fetus is a ________. Provide a few examples

teratogen

• alcohol

• viruses

• industrial chemicals

• antibiotics

• cocaine

What are prenatal diagnostic tests?

medical tests during pregnancy used to detect fetal abnormalities, genetic disorders, & well-being

List the 4 prenatal diagnostic tests

1. Fetal Ultrasonography

2. Amniocentesis

3. Chorionic Villi Sampling

4. Maternal alpha-fetoprotein (AFP)

Describe Fetal ultrasonography

• determines a more accurate fetal age when the date of conception is in doubt

  • also…

    • confirms pregnancy

    • determines fetal position

    • identifies multiple pregnancies

Describe Amniocentesis

• involves removing some amniotic fluid surounding the developing fetus, & analyzing it & fetal cells for genetic abnormalities

• needle used to collect the fluid is guided by ultrasound to avoid damage to fetus or umbilical cord

Describe Chorion Villi Sampling

• done under ultrasound guidance, but usual procedure is to insert a catheter through the vagina & cervix to collect a tissue sample from the chorionic villi

• goal → identify same genetic defects as seen w. amniocentesis

  • procedure may be done thru the abdominal wall as w/ amniocentesis

Describe Maternal Alpha-fetoprotein (AFP)

• requires blood sample from mother

  • detects AFP (a protein produced by the fetus at its highest levels between weeks 12-15) after the 16th week of pregnancy — when levels go to zero

  • after the 16th week, high levels of AFP indicate a neural tube defect (birth defects of the brain, spine, or spinal cord; happen during 1st month of pregnancy)

  • to interpret, must know gestational age, twin status, maternal health status, & race

During the 1st 3-4 months of pregnancy, the corpus luteum secretes _____ & _______ in low levels

progesterone

estrogens

From the 3rd month to the end of pregnancy, the placenta produces high levels of _____ & ________

progesterone

estrogensT

The ______ secretes ______ to stim. the corpus luteum to produce estrogens & progesterone to inhibit menstruation until the placenta takes over

chorion

hCG

List the hormones that the placenta secretes during pregnancy

1. Human Chorionic Gonadotropin (hCG)

2. Progesterone/estrogens

3. Relaxin

4. Human Choorionic Somatomammotropin (hCS)

5. Corticotropin-releasing hormones

Describe the function of hCG duirng pregnancy

rescues corpus luteum from degeneration until the 3-4 month of pregnancy

Describe the 3 functions of progesterone/estrogens during pregnancy

1. maintains endometrium

2. prepares mammary glands for lactation

3. prepare mother’s body for birth of baby

Describe the 2 functions of relaxin during pregnancy

1. increase flexibility of pubic symphysis

2. helps dilate uterine cervix during labour

Describe the 3 functions of Human Chorionic Somatomammotropin (hCS) during pregnancy

2. prepares mammary glands for lactation

3. enhances growth by increasing protein synth.

4. decreases glucose use & increases fatty acid use for ATP production

Describe the 2 functions of Corticotropin-releasing hormone during pregnancy

1. establishes the timing of birth

2. increases secretion of cortisol → needed for maturation of fetal lungs

define labor

process that expels the fetus from the uterus thu the vagina

List the 3 requirements for labor to begin

1. oxytocin must be released

2. estrogen elvels must rise

3. effects of progesterone must be inhibited

Contrast True labor & False labor

• true labor → begins when uterine contractions occur at regular intervals

• false labor → associated w/ irregular contractions & no “show” (a discharge of blood w/ mucus)

True labor is divided into 3 stages:

2. Stage of dilation

3. Stage of expulsion

4. Placental stage

Describe the respiratory adjustments of infants at birth

• lungs able to exchange oxygen & CO2 thanks to surfactant

• repiratory rate at birth drops from 45 breaths/min to the normal 12 breaths/min within 2 weeks

Describe the cardiovascular adjustments of infants at birth

• foramen ovale closes to become the fossa ovalis (in heart)

• ductus arteriosus closes to become the ligamentum arteriosum (in heart)

• umbilical arteries fill w/ connective tissue

• umbilical vein becomes the ligamentum teres of the liver

______ (secreted by the anterior pituitary) is the main hormone in stim. milk production

prolactin (PRL)

The hormone, _____, causes release of milk into the mammary ducts via the _______

oxytocin

milk ejection reflex

Describe the milk ejection reflex (positive feedback loop)

1. stimulation: suckling of baby on nipple

→ causes increasing

2. controlled condition: touch sensations

3. receptors: touch-sensitive sensory neurons in nipple

→ input: nerve impulses

4. control center: hypothalamus & posterior pituitary

→ output: increased oxytocin in blood

5. effectors: myoepithelial cells in mammary glands

→ contraction of myoepithelial cells

6. response: milk ejection

7. (possible interruption of cycle: baby ceases to suckle)

8. positive feedback: milk availibility encourages continued suckling, so touch sensations on nipple & oxytocin release continue

List the benefits associated w/ breast feeing an infant

• chem. composition of mother’s milk is ideal for the baby’s brain development, growth, & digestion

• several types of WBCs are in the milk → immunity

• antibodies present

• reduction in several diseases

define inheritance & genetics

inheritance → passage of hereditary traits from one generation to the next

genetics → study of inheritance

What is a punnett square used for

to show the possible genes inherited from 2 parents

Define allele

genes for the same trait that are in the same location on each homologue

Define genotype vs phenotype

• genotype → actual genetic makeup relating to a trait

• phenotype → physical expression of the genotype

Define dominant vs recessive (allele)

• dominant (allele) → allele that dominates or masks the presence of another allele; represented by UPPERCASE letter

• recessive (allele) → allele whose presence is completely masked; represented by lowercase letter

Define homozygous vs. heterozygous

• homozygous → 2 identical alleles for a gene (e.g. AA)

• heterozygous → 2 diff. alleles for a gene (e.g. Aa)

Define incompelte dominance

situation where neither member of the pair of alleles is dominant over the other

e.g. sickle cell anemia

Describe mutiple-allele inheritance

• occurs when genes have more than 2 alternative forms

  • e.g. inheritance of the ABO blood group

Describe polygenic inheritance

when a trait is controlled by the combined effects of 2+ genes

Describe complex inheritance and lsit examples of complex traits

when a trait occurs due to the combined effects of many genes & environmental factors

• complex traits:

  • skin, hair, eye colour

  • height

  • metabolic rate

  • body build

Define karyotype

entire set of chromosomes arranged in decreasing size order & according to the position of the centromere

The 23 pairs of human chromosomes include ____ pair(s) of _____ & ___ pair(s) of _______

22

autosomes

1

sex chromosomes (X & Y)

List the sex chromosomes that correspond to male and female & explain what determines the gender of the zygote

male → X & Y

female → 2 X (one is automatically inactivated)

• whether the sperm that fertilizes an egg carries an X or Y chromosomes determines teh gender of the zygote

A person who is heterozygous for a recessive gene will…

1. show the recessive phenotype

2. possible have child who shows the recessive phenotype

3. have 2 identical alleles

4. show a mutation of one allele

5. act as a carrier of the recessive gene for male offspring

Explain why mitochondrial DNA comes from the mother

1. mitochondria are in cytoplasm of cell

2. egg cell (mother) contributes a lot of cytoplasm and, resultantly, a lot of mitochondria

3. sperm cell (father) contributes mostly just its nucleus (DNA)

4. the sperm’s mitochondria either don’t enter the egg or are broken down after entry

Explain how to analyze a karyotype to detect genetic defects

1. count chromosome → normal = 46 total

2. check for trisomy (3 copies of chromosome) or monosomy (only 1 copy)